Check the air filter, and change it when dirty

A clogged filter makes the system work harder and wear faster.

Who: You can do it yourself. Electronic, UV or air-scrubber filters: an HVAC technician may need to install or service them.

How often: Check monthly, year round; replace 1-inch fiberglass about every 30 days, 1-inch pleated every 1-3 months, 4-5 inch media every 6-12 months, and check more often in wildfire-smoke season. For: the furnace, air conditioner, heat pump.

Safety first

Turn the system off at the thermostat or the furnace’s power switch.
If the filter is behind the blower door or in a media cabinet, disconnect power to the unit first.
Never run the system with no filter in it.
Don’t wash a disposable pleated or media filter; wash only a filter sold as washable.
Don’t move to a thicker or higher-MERV filter unless your system’s manual allows it; use the size and type it came with.

What you need

A filter of the same size and type as the old one.
A screwdriver, if the filter sits behind a screwed-on return grille.

The part, and finding the right one

Air filter. Check it monthly; replace 1-inch fiberglass about every 30 days, 1-inch pleated every 1-3 months, a 4-5 inch media filter every 6-12 months. The size is printed on the edge of the filter you have now (for example 16 x 25 x 1). Buy the same size.

On a home’s record, each piece of equipment’s page links its manual and a search for its parts by brand and model. All filters and parts

How to do it

Find it: a slot about an inch wide with a hinged or removable cover on the furnace or air handler, usually in the blower compartment near the bottom. If it isn’t there, look behind a return-air grille (some homes have one behind every return grille).
Note which way the arrow on the frame points, then slide the filter out.
Hold it up to a light. If light doesn’t pass through, or it’s gray and coated in dust, replace it.
Buy the size printed on the frame (for example 16 x 25 x 1). The printed size can be a half inch bigger than the real one, so match what is printed.
Slide the new one in with the arrow toward the furnace or blower. Old filter has no arrow? Drag a finger across both sides: the dirtier side faced the incoming air.
Close the cover, restore power, and listen for normal running.
Write today’s date on the frame.

If yours is a 4-5 inch media cabinet (a tall box beside the furnace)

Disconnect power.
Pull the door handle toward you to swing the door open; lift slightly and remove the door.
Note which way the AIR FLOW arrow points, and pull the old cartridge out.
Slide the new one in with the arrow toward the furnace, and write the install date on the cartridge.
Put the door’s tab in the slot, swing it closed and press firmly; reconnect power.
This is Honeywell’s routine; another brand’s cabinet follows its own manual.

Normal

A filter that looks dirty at the monthly look: change it; nothing more.

Needs attention

After a fresh filter, the furnace keeps starting and stopping in short bursts. Makers’ thresholds differ (Carrier: under 5-10 minutes; Trane: under 7; Bryant: normal is 10-15 minutes or longer), and on a very cold night frequent cycling can be normal.

Call an HVAC technician if

Short cycling that continues after a fresh filter and a check of the thermostat and its batteries.
New or excessive noise after a filter change.

Keep

The date on the frame.

Keep track of it

Add your home to My homes: each piece of equipment gets this on its own schedule, with “Mark done” and reminders you can turn on.

Find your home Sign in

Sources

Your owner’s manual comes first: where it says something different for your model, follow it.

Still stuck?

Email us at hello@tradewrench.com. Tell us which page you were on and what you were trying to do.

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